The present invention pertains to resonant integrated microstructure (RIM) sensors, and particularly to high temperature resonant integrated microbeam sensor.
An electrical RIMS sensor is shown in FIG. 1. Microbeam 11 vibrates at a resonant frequency of its structure. Beam 11 is supported by posts 12 which are a part of a micromachined silicon-based device 16. Beam 11 is driven electrostatically by a capacitive plate 13 which is proximate to the center of the beam and electrostatically causes the beam to flex or vibrate in a direction towards and away from capacitor 13. Sensing of the frequency of beam 11 is performed by a piezoresistor 14 embedded in beam 11. Drive/sense electronics 25 provide electrical signals to capacitive plate 13 for driving beam 11 and receive electronic signals from sensor 14 which are processed to indicate the frequency of beam 11. One disadvantage of a sensor 16 is that it cannot function well at temperatures above 200 degrees Centigrade (C.). For example, piezoresistor sensors fail at temperatures less than 250 degrees C.
Besides the electrical RIMS system 16, there is also an optical RIMS 17 that is also similarly inadequate for sensing parameters in high temperature environments. Similarly, system 17 has a resonant beam 11 held by supports 12 which are a part of a micromachined integrated silicon device. A light emitting diode (LED) or laser 18 emits light 19 via optical fiber 20 through beam 11 onto a photo diode 21 which is situated beneath beam 11. When photo diode 21 receives light 19, it generates an electrical charge which then electrostatically attracts beam 11 thereby causing it to vibrate at its natural frequency. Light 22 is reflected off of photo diode 21 and beam 11 and is transmitted via fiber 23 to a photo diode 24 which is connected to drive/sense electronics 25. Electronics 25 processes light signals 22 for determining the actual vibrating frequency of the resonant beam, which is a comparison of signals 22 and determination of the beat frequency between signals 22 reflected from photo detector 21 and beam 11, respectively, and also for determining and providing an appropriate drive signal to maintain the vibration of the beam. This system 17 also is incapable of functioning under high temperature environments. For example, photo diodes fail at temperatures less than 250 degrees C.